from the nickel(II) center with the inner C–H bonds and the axial Ni–Cl bond in an
anti-orientation. As demonstrated by the analysis of the line width of the 5-NiCl
1
H
NMR spectra, the trace amounts of syn conformers rapidly equilibrate with the
respective anti forms [56].
A similar acid-controlled rearrangement was noticed for palladium(II) mesoalkylidenyl m-benziporphyrin [66]. Other meso-alkylidene m-benziporphyrin complexes contain nickel(II) or silver(I) ions (Scheme 32) [66]. In the presence of bulky
exocyclic double-bond paramagnetic modified high-spin nickel(II), m-benziporphyrin
23-NiCl was formed. The diamagnetic silver(I) complex 23-Ag was stabilized via the
coordination of two pyridine molecules as axial ligands.
The relevant X-ray-determined molecular structures of 5-Pd and 5-NiCl exemplifying in-plane [57] and side-on [16] coordination motifs are shown in Fig. 1. The
representative molecular structures for aza-m-benziporphyrin complexes 3-Zn [22]
and 4-Fe [89] are presented in Fig. 2.
N
N
N
Ar
Ar
Ph
Ph
Ni
N
N
N
Ar
Ar
Ar
Ar
Ni
5-Ni
5-NiCl
HCl
base, Δ
Cl
Scheme 31 Fundamental
structures 5-Ni-and 5-NiCl
involved in acid-controlled
equilibrium
H
N
N
N
Ar
Ar
EtO 2 C
EtO 2 C
CO 2 Et
CO 2 Et
N
N
N
Ar
Ar
EtO 2 C
EtO 2 C
CO 2 Et
CO 2 Et
N
N
N
Ar
Ar
EtO 2 C
EtO 2 C
CO 2 Et
CO 2 Et
Ni
Pd
Cl
N
N
N
Ar
Ar
EtO 2 C
EtO 2 C
CO 2 Et
CO 2 Et
Pd
X
TFA
23
23-Pd
23-Pd-X
23-NCl
Ni(II)
Pd(II)
Ag(I)
Ar = p-Tol or C 6 F 5
N
N
N
Ar
Ar
EtO 2 C
EtO 2 C
CO 2 Et
CO 2 Et
Ag
L
23-Ag
L
L = 2,6-dimethylpyridine
Ar = C 6 F 5
Ar = C 6 F 5
X = OCOCF 3
Scheme 32 Nickel(II), palladium(II), and silver(I) meso-alkylidenyl m-benziporphyrins – formation and protonation [66]
A Pincer Motif Etched into a meta-Benziporphyrin Frame
203